The term 'ketogenic DIET' refers to a high-fat, low-carbohydrate DIET that is used to treat certain medical conditions. It is also sometimes referred to as a 'keto DIET'. The DIET works by forcing the body to burn fat instead of carbohydrates for energy, resulting in a state of ketosis. This DIET has been used to treat epilepsy, diabetes, and other metabolic disorders. It has also been used as a weight loss tool. The four letter solution to the crossword puzzle is DIET.